Bulk material nuclear moisture gauging system

ABSTRACT

An improvement on a moisture gauging system of the type disclosed in Stone et al. U.S. Pat. No. 3,431,415, issued Mar. 4, 1969, in which slow neutrons are sensed to provide an indication of the moisture and other neutron interacting material content of an irradiation volume of a substance. A compensation circuit is provided to counteract the effect of neutron interacting material in the substance under test.

United States Patent [191 Kylin et al.

BULK MATERIAL NUCLEAR MOISTURE GAUGING SYSTEM Republic SteelCorporation, Cleveland, Ohio Filed: Feb. 2, 1972 App]. No.: 222,967

Related US. Application Data Continuation-impart of Ser. No. 34,730, May5, 1970, abandoned.

Assignee:

[ 1 Jan. 15, 1974 [56] References Cited UNITED STATES PATENTS 3,435,2173/1969 Givens 250/831 3,529,160 9/1970 Moran 250/83.l

Primary Examiner-Archie R. Borchelt Attorney-R0bert P. Wright et a1.

[57] ABSTRACT An improvement on a moisture gauging system of the typedisclosed in Stone et al. US. Pat. No. 3,431,415, issued Mar. 4, 1969,in which slow neutrons are sensed to provide an indication of themoisture and other neutron interacting material content of an irra- F 'g250/43'5 g gg' gg f s g diation volume of a substance. A compensationcircuit r 2 is provided to counteract the effect of neutron interle 0 Eacting material in the substance under test.

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BULK MATERIAL NUCLEAR MOISTURE GAUGING SYSTEM CROSS REFERENCE TO RELATEDAPPLICATION This application is a continuation-in-part of our copendingapplication Ser. No. 34,730, filed May 5, 1970 for Nuclear GaugingSystem, now abandoned.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION This invention relatesto a nuclear moisture gauge. There is disclosed herein an improvement ona bulk material moisture gauging system of the type disclosed in Stoneet al. U.S. Pat. No. 3,431,415, issued Mar. 4, 1969. The bulk materialmositure gauging system disclosed in the aforesaid patent comprises asource of fast neutron and gamma radiation for irradiation of acrosssectional volume of a bulk substance.

The improvement herein permits application of the previously describedsystem to the measurement of the moisture content of materials havingneutron interacting elements in addition to water, whether such materialmoves in a stream of irregular and varying crosssection or whether suchstream of material has a regular cross-section. A circuit is providedwhich produces the correction which is needed in compensating for theextra neutron-moderating effects produced by neutron collision withelements such as carbon which could interacttmoderate or absorb)-withthe neutron flux to produce an erroneous measurement of moisture.

The invention of the above application was conceived in connection withthe gauging of the moisture content of metallurgical coke. It is,however, equally adapted to the measurement of moisture in othersubstances; to mention only a few of them: moisture in cereal, moisturein coal, moisture in sugar, moisture in plastics, moisture in limestone,and moisture in paper pulp.

Moreover, the number of neutron interacting elements which can introduceerrors into the gauge output are numerous. They include, among others,hydrogen, deuterium, helium, lithium, beryllium, carbon, oxygen, uraniumand iron.

For background in consideration of the present invention, referenceshould be made to the aforenoted system described in U.S. Pat. No.3,431,415, assigned to the assignee of the present invention. Thatpatent describes a nuclear moisture gauge for measuring, indicating andcontrolling the moisture in moisture containing solids. As stated, thatinvention was developed and applied to the measurement and control ofmoisture in sinter mix materials as they are transported on a conveyorbelt, and it has been applied to a variety of such materials. However,it has been found that in the case of metallurgical coke or other highlycarbonaceous material, as well as other materials with which neutronsmay interact, accurate measurements of moisture content are notobtainable due to the fact that correction is needed in order tocompensate for the fact that the carbon contained in coke or otherhighly car bonaceous material and similar neutron interacting ma;-terials produces extra neutron-moderating effects. Without suchcompensation the signal obtained from the neutron detector will be inerror because the interacting materials present in coke, or likematerial, act to slow the neutrons in the same way as the hydrogenpresent in water, thereby giving an erroneous indication of moisturecontent which is the desired parameter being measured.

Accordingly, it is a primary object of the present invention to enableaccurate measurement and indication of the moisture content, by weightpercentage, of substances containing significant quantities of neutroninteracting materials.

A presently preferred embodiment of the invention is incorporated in asystem of the: type shown in U.S. Pat. No. 3,431,415, i.e., in amoisture gauging system utilizing a source of fast neutron and gammaradiation for irradiation of a cross-sectional volume of a bulksubstance. There is provided in the system a slow neutron responsivemeans responsive to slow neutrons from the cross-sectional volumeirradiated by neutrons for deriving a first electrical control energyvarying with the moisture content of an irradiation volume of thesubstance, gamma responsive means positioned to receive gamma radiationwhich emanates from the source and traverses a volume irradiated bygamma radiation for deriving a second electrical control energy varyingwith the mass of the substance in an irradiation volume thereof, andmeans jointly responsive to the first and second electrical controlenergies for obtaining the ratio existing between said first and secondcontrol energies and for generating an output signal proportional to theweight percentage: moisture content of said substance. In such a systemthere is included, in accordance with the present invention, means forcompensating for the presence of neutron interacting elements in thebulk substance other than the hydrogen of the water content.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of thenuclear moisture gauge of U.S. Pat. No. 3,431,415;

FIG. 2 is a block diagram of an improved nuclear moisture gauge whichcompensates for neutron interacting elements in accordance with thepresent invention;

FIGS. 3, 4 and 5, taken together, comprise a schematic diagram of acircuit embodying the present invention.

DETAILED DESCRIPTION In FIG. I of the drawings, there is depicted ablock diagram of the nuclear moisture gauge previously disclosed in U.S.Pat. No. 3,431,415, assigned to the assignee of the present invention.FIG. 1 herein is the same as FIG. 2 of the patent. Reference may be madeto that patent for a detailed description of such gauge and anassociated moisture control system.

Briefly considered, the gauge shown in FIG. 1 comprises a neutrondetector and a gamma detector so designed and interconnected as toproduce an output signal proportional to the weight percentage moisturecontent of the material being measured substantially independently ofthe geometry of the material in the stream of material being gauged. Thegamma detector detects any changes in the weight of the material, whilethe neutron detector detects moisture changes directly by measuring theslowing of neutrons which have irradiated the material. Means areprovided jointly responsive to the electrical control energies resultingfrom the neutron detection and the gamma detection so as to obtain theratio existing between the two control energies.

FIG. 2 is a block diagram of an improved nuclear moisture gauge. Thegauge shown in FIG. 2 comprises the gauge just described and a newcompensator circuit for neutron interacting elements. The neutrondetector detects both moisture change and weight changes of the neutroninteracting elements directly by measuring the slowing of neutrons whichhave irradiated the material. The neutron amplifier is madenon-responsive to the weight changes of the neutron interacting elementsby introducing a compensation signal derived from the gamma detectionand representative of mass. Means are provided jointly responsive to theelectrical control energies resulting from the detection as compensatedand the gamma detection so as to obtain the ratio existing between thetwo control energies.

The invention herein is most readily understood by first considering theneutron detector and amplifier and the gamma detector and amplifier, asshown in FIGS. 3, 4 and 5. The circuits shown in FIGS. 3, 4 and 5 arethe same as those shown respectively in FIGS. 10, 11 and 12 of US. Pat.No. 3,431,415, except for the additon of compensation circuit 200 ofFIG. 4. While reference may be made to the patent for the details of thecommon features of the circuits, the following explanation is given bothto simplify understanding of all features and to explain the operationof the compensation circuit 200.

As shown very clearly in FIG. 3, the neutron detector includes a groupof six boron trifiuoride proportional counter tubes V3-V8 having anodesand cathodes connected in parallel and energized through a resistor R9of relatively large value from a unidirectional high voltage powersupply system. The latter is of conventional half-wave rectificationtype, and is regulated by inclusion in its output circuit of a seriesregulating resistor R8 and a shunt-connected regulating tube V1. Theresistor R9 provides constant-current limiting for the neutron detectortubes, and also provides for the latter a load resistor across whichpotential pulses are developed when the neutron detectors are subjectedto slow neutron bombardment. The number of potential pulses developed bythe neutron detector tubes across the resistor R9, in response to theslow neutron bombardment of the detector tubes, is proportional to thequantities of moisture and neutron interacting elements in the materialbeing gauged with different constants of proportionality. These slowneutrons which pass the detector tubes without being detected arereflected back to the neutron tubes by carbon blocks (not shown) mountedunder the tubes.

The neutron detector tubes V3-V8 are insensitive to fast neutrons, butdo produce relatively small amplitude potential pulses across theresistor R9 in response to gamma radiation. As will presently beexplained more fully, the effect of these small potential pulses isnullified by an amplitude limiting characteristic provided in theneutron amplifier hereinafter described.

The voltage pulses developed by the neutron detector tubes V3-V8, acrossthe resistor R9, are coupled through a condenser C6 to the baseelectrode of a transistor 01 included in the first stage of aconventional two-stage alternating-current transistor preamplifier. Thisamplifier is energized from a low-voltage full-wave rectifier system,shown at the top of FIG. 3, having its output voltage regulated by aZener diode device D3. The second amplifier stage includes a transistorQ2 operating as an emitter-follower arrangement by reason of the directconnection of its collector electrode to the low-voltage energizingsource and by use of an unbypassed resistor R16 in its emitter electrodecircuit. The transistor preamplifier amplifies the potential pulsesdeveloped across the resistor R9 of the neutron detector tubes V3V8, andthe amplified potential pulses developed across the emitter resistor R16of the second stage are coupled through a condenser C9 and a coaxialcable L10 to the primary winding of a transformer T3. The emitterresistor R16 has a value of resistance selected in conventional mannerto match the output driving impedance of the preamplifier secondtransistor stage to the input impedance of the cable L10, which has itsimpedance also matched to the input impedance of the primary winding ofthe transformer T3.

The secondary winding of the transformer T3 is coupled through acondenser C10 (FIG. 4) to the base electrode of a transistor Q3,employed as the first stage of a two-stage neutron transistor amplifier,to apply the output potential pulses of the tranformer T3 asnegative-polarity pulses to the base electrode. The first transistorstage includes a collector load resistor comprised by the resistiveelement of a potentiometer R18 across which amplified positive-polaritypotential pulses are developed. The base electrode of the transistor Q3is conventionally biased as shown by a degenerative bias arrangementincluding a potential divider comprised by series-connected resistorsR17 and R19 connected from the collector electrode of the transistor Q3to ground. The transistor O3 is protected from excessiveamplitude inputvoltage pulses by diode rectifier devices D5 and D6 connected withopposite conductive polarities across the secondary winding of thetransformer T3.

The second stage of the neutron amplifier provides pulse amplificationand wave shaping, and is a conventional monostable multivibrator whichincludes transistor devices Q4 and Q5 utilizing a common emitterresistor R24 and having the collector electrode of the transistor Q4coupled through a condenser C13 to the base electrode of the transistorQ5. The base electrode of the transistor Q5 is biased by a resistor R25to a potential which normally renders the transistor Q5 conductive, andthe resultant potential produced across the emitter resistor R24 by theconductive current of the transistor Q5 biases the transistor O4 to anormally non-conductive state. The multivibrator arrangement has itsoperational characteristics conventionally stabilized by use of acompensating diode rectifier D8 serially included in the degenerativebase-bias potential divider comprised by the series resistors R21 andR22. The base electrode of the multivibrator transistor Q4 is coupledthrough a condenser C11 to the movable contact of the potentiometer R18,which may be manually adjusted to select a desired porportionate part ofthe amplified pulse voltages developed across the potentiometerresistive element by the transistor Q3 of the first amplifier stage. Adiode rectifier device D7 is connected, with the conductive polarityshown, between the base electrode of the multi-vibrator transistor Q4and ground potential to provide bias stabilization.

Manual adjustments of the adjustable contact of the potentiometer R18enables the input circuit of the transistor Q4 to discriminate againstthe lower amplitude potential pulses produced by gamma radiation of theneutron detector tubes v3-V8. In particular, the pulse amplitudediscrimination thus effected by adjustment of the potentiometer R18 issuch that only the amplified neutron potential pulses developed by theneutron detector tubes V3-V8 have sufficient amplitude to operate themonostable multivibrator, comprising transistors Q4 and Q5, through acycle of its operation.

Each cycle of operation of the transistor multivibrator just describedproduces a short-duration positive potential pulse across a loadresistor R26 included in the collector electrode circuit of thetransistor Q5. These potential pulses are coupled through a condenserC14 to a pulse integrating circuit comprised by a shunt-connected diodeD9 and a series-connected diode D10, having the conductive polaritiesshown, and including an output-circuit shunt condenser C15 and shuntresistive potential divider comprised by a resistor R27 connected inseries with the resistive element of a span potentiometer R28. Thecircuit values of this output circuit are selected to provide a timeconstant such that the potential output pulses of the multivibrator areso integrated in the output circuit as to produce across thepotentiometer R28 an output unidirectional voltage having a valuevarying linearly with the rate of the neutron detector pulses appliedthrough the input transformer T3 to the neutron transistor amplifier.

The unidirectional voltage across R28 varies linearly with the rate ofthe neutron detector pulses when switch S2 is open, that is, when thecompensator is not active. When the compensator is activated by closingswitch S2, the voltage across R28 is increased or decreased by an amountproportional to the position of the sliding contact of retransmittingslidewire R208. The action of the compensator will presently beexplained more fully.

A proportionate part of this unidirectional potential, selected by theadjusted position of the movable contact of the span-potentiometer R28,is compared against a zero reference value of unidirectional potentialselected by the adjusted position of a potentiometer R32 having itsresistive element serially connected with a resistor R3] across thesource of unidirectional voltage which energizes the neutron amplifier.In particular, the span-potentiometer and zeroreference potentiometervoltages have like polarity with respect to ground potential and areapplied in series opposing relation with one another to the inputcircuit of a recorder amplifier RA-10. This input circuit includes aninput transformer T12 having a secondary winding connected to the inputcircuit of the recorder amplifier RA-10 and having a center tappedprimary winding with the center tap thereof connected through thenormally closed contacts 1 and 2 of a calibrating relay RLl to themovable contact of the span-potentiometer R28. The end terminals of theprimary winding of the input transformer T12 are connected to thestationary contacts of a vibrator, these contacts being alternatelyengageable by the vibrator movable contact which is actuated by sixtycycle electrical energization of a vibrator energizing winding VC 10from a low voltage energizing circuit of the recorder amplifier RA-lO.The movable contact of the vibrator is connected through the normallyclosed contacts 1 and 2 of a calibrating relay RL-2 to the movablecontact of a recorder slide wire potentiometer R35 having an endterminal connected as shown through normally closed contacts 4 and 5 ofthe relay RL-2'and normally. closed contacts 1 and 2 of a calibratingrelay RL-l0 to the movable contact of the zero-reference potentiometerR-32.

The gamma detector includes a group of 10 halogen quenched geiger tubesV9-V18 (FIG. 5) which are individually energized through respectiveresistors R67-R76 from a regulated high voltage power supply system.This power supply system is of conventional half-wave rectification typehaving a series regulating resistor R64 and shunt regulating tube V2,and has its positive output terminal connected through the centralconductor of a coaxial transmission line L11 to the resistors R67-R76for positive energization of the centrally positioned coaxial electrodeof the respective geiger tubes V9-V18. The outer concentric electrodesof these tubes are connected in common to the negative terminal of thehigh voltage supply system through a series circuit which includes theouter concentric conductor of the transmission line Lll and a condenserC29, the latter having connected in parallel thereto a series resistivecircuit including a resistor R61, the resistive element of apotentiometer R62, and a resistor R63. The geiger tubes V9-V18 arephysically positioned to survey approximately the same detection area asis surveyed by the neutron detection tubes V3-V8 earlier considered, andvoltage pulses are produced across the condenser C29 and resistors R61R63 by the geiger tubes V9-V18 when the latter are subjected to gammaradiation. The number of voltage pulses so produced per unit of time isproportional to the amount of radiation passing through the material onthe conveyor belt. Since the density of any given material issubstantially constant, the number of voltage pulses produced across thecondenser C29 and resistors R61-R63 by the geiger tubes V9-V18 isinversely proportional to the weight of the material on the conveyorbelt.

The voltage pulses produced by the geiger tubes V9-Vl8 are integrated bythe resistive-capacitive network comprised by the condenser C29 andresistors R61-R63 to produce across the potentiometer R62 and resistorR63 a unidirectional voltage having a value proportional to the numberof voltage pulses produced by the geiger tubes V9-V18 per unit of time.The movable contact of the potentiometer R62 may be manually adjustedalong the length of the potentiometer resistive element to select andapply to the base electrode of a transistor Q7 a fractional part of theunidirectional voltage developed by integration across the potentiometerR62 and resistor R63. The transistor Q7 is included with a transistor O6in a conventional two-stage compound-connected transistor amplifier inwhich the collector electrodes of the transistors Q6 and Q7 areenergized through a resistor R from a conventional full-wave powersupply system having its output regulated by a shunt zener device D23and a series resistor R77.

The emitter electrode of the transistor Q7 is directly connected to thebase electrode of the transistor Q6, and the emitter electrode of thelatter is connected to ground potential through a resistor R59 and astabilizing series diode rectifier D22. The transistor Q6 operates as anemitter-follower amplifier stage to develop across the emitter resistorR59 and diode D22 the amplified unidirectional voltage applied to thebase electrode of the transistor Q7, a condenser C28 being connected inshunt to the emitter resistor R59 and diode D22 to bypass anysignificant alternating-current frequency components appearing in theamplified output voltage.

The amplified unidirectional output voltage of the transistor stage Q6is supplied through an adjustable span resistor R58, normally closedcontacts 1 and 2 of a calibration relay RL-6, and the normally closedcontacts 4 and 5 of the relay RL-2 (FIG. 4) to one terminal of theresistive element of the recorder slide wire potentiometer R35 as shown.The opposite terminal of the resistive element of the potentiometer R35has a zero reference voltage applied to it from the adjustable contactofa zero reference potentiometer R47 (FIG. 5) which is connected with afixed resistor R46, an adjust able resistor R48, and parallel connectedresistors R49- R51 across the source of unidirectional voltage whichenergizes the compound transistor amplifier just described. The zeroreference voltage thus applied to one end terminal of the recorder slidewire potentiometer R35 has the same positive polarity with respect toground potential as does the amplified unidirectional output voltageapplied to the other terminal of the potentiometer R35 by the compoundtransistor amplifier comprised by the transistors Q6 and Q7. Thus thenet voltage developed across the recorder slide wire potentiometer R35corresponds to the prevailing difference between the zero referencevoltage and the amplified output voltage of the gamma detectoramplifier.

The automatic recalibration of the neutron and gamma detectors justdescribed can be accomplished in the manner described in U.S. Pat. No.3,43l,415 (see Col. 6 thereof). The compensator offset switch S1 (FIG. 4herein) comprising sections S1A and SIB and the compensator spanpotentiometer R210 are adjusted during initial calibration of thesystem. They are not a part of the automatic calibration system of U.S.Pat. No. 3,431,415. Controls S1 and R101 are set at the same time as thetwo calibration reference voltages (potentiometers R41 and R42, FIG. 17of U.S. Pat. No. 3,431,415). The settings of S1, R210, R41 and R42depend on the normal material weight and moisture, the type of conveyorbelt, and the material being gauged at a particular installation of thisinvention.

Referring specifically to FIG. 4, it will be noted that the compensationcircuit in accordance with the present invention appears in the lowerleft corner thereof. This compensation circuit is designated 200 and isconstructed to enable accurate measurement of moisture content despitethe fact that carbonaceous and/or other neutron interacting materialsare involved. In other words, the compensation circuit is used when thematerial to be gauged includes neutron interacting elements other thanthe hdyrogen in the moisture such as metalurgical coke, or the like, toadapt the gauging system to compensate for the error that is introducedby the presence of the interacting elements, such as carbon, or thelike.

It will be seen that the upper end of the neutron span potentiometer R28is connected to the compensation circuit through resistor R202 forming apart thereof. The switch S2 is used to include the compensation circuitwhen desired, that is, when carbonaceous material or other neutroninteracting material is present.

The compensation circuit 200 comprises a voltage divider network havingtwo legs 204 and 206 connected to a weight recorder retransmittingslidewire potentiometer designated R208, a switch designated S1, a spanadjusting potentiometer designated R210,

and coupling resistor R202 and coupling switch S2. Each of the legs 204and 206 comprises a group of resistors serially connected. The ends of204 and 206 not connected to R208 are connected to potential supplies oftypical values plus 30 volts and minus 30 volts respectively. The weightrecorder (not shown) responds to the output of the gamma amplifier andcontains appropriate zero and span adjustments. The weight recorder spanand zero adjustments are set such that the sliding contact 208a is at 0%when no material is being gauged and at 100% when a maximum amount isbeing gauged. In other words, the setting of the potentiometer R208varies with the mass of the gauged material.

The resistors in legs 204 and 206 are selected to have a value ofapproximately 250 ohms each. A slidewire potentiometer R208 has a valueof approximately 1,000 ohms.

The basic compensator signal is developed at the slide contact 208a ofthe slidewire potentiometer R208. It is evident that this signal becomesmore negative in direct relation to the increase in neutron interactingmaterial weight in the gauging zone. As will be explained more fully,this compensator signal offsets the portion of the neutron detectorsignal that becomes more positive with increasing neutron interactingmaterial weight.

The switch S1 forming part of the compensator is a two-section device,the sections being designated S1A and $18. The mechanical linkagebetween the two switch sections is shown by the dash line on the drawiwill be evident that the electrical zero point of the compensator outputis determined by the switch S1 and that in any position of switch S1 theoutput will become more negative as the material mass increases. Thecorrelation between the position of switch S1 and the percentage ofweight span for zero compensation will be seen from the following table:

PERCENT OF WEIGHT SPAN S1 POSITION FOR ZERO COMPENSATION To verify thetable let it be assumed that the switch S1 is placed in the firstposition; that is, that the movable contacts of the sections S1A and SIBare both touching their respective fixed contacts 1, then none of theresistors in leg 204 is shorted out by section S1A, whereas all of thesections in leg 206 are shorted out. Consequently, a negative potentialof 30 volts extends at the right hand end of the slide wire resistor.Therefore, the electrical zero point is at the left end of the slidewire resistor.

At the other extreme position, that is, position 5 for the switch S1,the electrical zero point will be at the right end of the slide wireresistor. At the intermediate switch positions, of course, the zeropoint will be at proportionate locations.

A fraction of the aforementioned compensator output signal developed atthe contact 208a is taken from the sliding contact of the compensatorspan control potentiometer R210. When the switch S2 is placed in theclosed position the signal taken from the sliding contact of thepotentiometer R210 is transmitted via resistor R202 and is combined atthe potentiometer R28 with the signal from the neutron amplifier. Thelatter signal represents the moisture content but includes an erroneouscomponent due to the neutron interacting atoms present in the materialbeing gauged. However, the resultant signal at the sliding contact ofR28 represents the true value of moisture content since it has beencompensated for such erroneous component.

In order to calibrate the compensation circuit 200 the control S1 isinitially set for zero compensation at the normal operating weight span.A typical run of dry material is made and R210 is adjusted with S2closed to remove the signal at R28 due to the atoms moderating theneutrons. Further refinements to the setting of R210 can be made atnormal moisture levels.

Having made the above-described calibration, the setting ofpotentiometer R210 remains valid even though the moisture content of themix varies. This is so because the error introduced by the neutroninteracting material is a fixed fraction of the material weight. Thecarbon in metallurgical coke, for example, is about 95 percent of thetotal weight of the material. However, should the percentage of neutroninteracting material in the mix differ significantly from the above, thecompensation network would be recalibrated.

It is to be understood that although this invention has been describedin terms of a representative, presently preferred embodiment thereof,modifications will be apparent to those skilled in the art. Theinvention should be taken to be defined by the following claims.

We claim:

l. A moisture gauging system for irradiation of a cross-sectional volumeof a bulk substance, slow neutron responsive means responsive to slowneutrons from said cross-sectional volume irradiated by neutrons forderiving a first electrical control energy varying with the moisture andother neutron interacting material content of an irradiation volume ofsaid substance, gamma responsive means positioned for irradiation bygamma radiation for deriving a second electrical control energy varyingwith the mass of said substance in an irradiation volume thereof, meansjointly responsive to said first and second electrical control energiesfor obtaining the ratio existing between said first and second controlenergies and for generating an output signa] proportional to the weightpercentage moisture content of said substance sustantially independentlyof the geometry of the material in the stream of material being gauged,and means for compensating for the presence of neutron interactingmaterial besides water in said bulk substance comprising a compensationcircuit responsive to said gamma responsive means and selectivelyconnectable to said slow neutron responsive means.

2. A system according to claim 1 in which said compensating meanscomprises a voltage divider network for providing a compensating signalsufficient to compensate for the error component of the signal from saidslow neutron responsive means.

3. A system according to claim 2, further including a plurality ofresistors, a source of positive potential, a source of negativepotential, and means providing an output signal which varies selectivelymore toward one polarity as the mass of the substance increases.

4. In a moisture gauging system for irradiation of a cross-sectionalvolume of a bulk substance, and including slow neutron responsive meansresponsive to slow neutrons from said cross-sectional volume irradiatedby neutrons for deriving a first signal varying with the moisture andother neutron interacting material content of an irradiation volume ofsaid substance, the combination therewith of gamma responsive meanspositioned for and responsive to irradiation by gamma radiation forderiving a second signal varying substantially only in accordance withthe mass of said substance in an irradiation volume thereof, and meansfor summing said first and second signals to produce a composite signalrepresentative substantially only of the moisture content of saidirradiation volume.

5. A system according to claim 4, in which the second signal is made tovary in a sense to reduce the composite signal for changes in saidsecond signal respresenting increases in the mass of said substance ofsaid irradiation volume.

6. A system according to claim 4, in which said substance iscarbonaceous material, and said gamma responsive means is responsive tothe presence of carbon in said carbonaceous material.

1. A moisture gauging system for irradiation of a crosssectional volumeof a bulk substance, slow neutron responsive means responsive to slowneutrons from said cross-sectional volume irradiated by neutrons forderiving a first electrical control energy varying with the moisture andother neutron interacting material content of an irradiation volume ofsaid substance, gamma responsive means positioned for irradiation bygamma radiation for deriving a second electrical control energy varyingwith the mass of said substance in an irradiation volume thereof, meansjointly responsive to said first and second electrical control energiesfor obtaining the ratio existing between said first and second controlenergies and for generating an output signal proportional to the weightpercentage moisture content of said substance sustantially independentlyof the geometry of the material in the stream of material being gauged,and means for compensating for the presence of neutron interactingmaterial besides water in said bulk substance comprising a compensationcircuit responsive to said gamma responsive means and selectivelyconnectable to said slow neutron responsive means.
 2. A system accordingto claim 1 in which said compensating means comprises a voltage dividernetwork for providing a compensating signal sufficient to compensate forthe error component of the signal from said slow neutron responsivemeans.
 3. A system according to claim 2, further including a pluralityof resistors, a source of positive potential, a source of negativepotential, and means providing an output signal which varies selectivelymore toward one polarity as the mass of the substance increases.
 4. In amoisture gauging system for irradiation of a cross-sectional volume of abulk substance, and including slow neutron responsivE means responsiveto slow neutrons from said cross-sectional volume irradiated by neutronsfor deriving a first signal varying with the moisture and other neutroninteracting material content of an irradiation volume of said substance,the combination therewith of gamma responsive means positioned for andresponsive to irradiation by gamma radiation for deriving a secondsignal varying substantially only in accordance with the mass of saidsubstance in an irradiation volume thereof, and means for summing saidfirst and second signals to produce a composite signal representativesubstantially only of the moisture content of said irradiation volume.5. A system according to claim 4, in which the second signal is made tovary in a sense to reduce the composite signal for changes in saidsecond signal respresenting increases in the mass of said substance ofsaid irradiation volume.
 6. A system according to claim 4, in which saidsubstance is carbonaceous material, and said gamma responsive means isresponsive to the presence of carbon in said carbonaceous material.